In recent years, as an examination apparatus used for ophthalmologic examination, an optical coherence tomographic image capturing apparatus (hereinbelow referred to as “anterior eye OCT”) which captures a tomographic image of a subject's eyeball (subjected eye) by an optical coherence tomography (OCT) is provided.
Specifically, the anterior eye OCT is used, for example, for glaucomatous examination. A main part of glaucomatous examination is angle analysis of a narrow-angled eye with primary angle closure or primary angle-closure glaucoma and a narrow-angled eye suspected to have primary angle closure or primary angle-closure glaucoma (for example, see Koichi MISHIMA, June, 2011. “Clinical Use of Anterior Segment OCT in Glaucoma”, Journal of the eye. Vol. 28, No. 6, pp. 763-768).
Generally, in the anterior eye OCT, a two-dimensional tomographic image of one sliced surface is acquired by scanning measurement light one-dimensionally relative to the subjected eye (B-scan), and then a three-dimensional image is obtained by acquiring two-dimensional tomographic images repeatedly while displacing scanning position of the measurement light (in other words, changing a sliced surface) relative to the subjected eye (C-scan).
As a scanning method, there is a method called raster scan as shown in FIG. 4A. In the raster scan, a one-dimensional scan along a scan line extending horizontally (B-scan) is performed repeatedly while moving in a vertical direction to other scan lines (C-scan). Due to this, as shown in FIG. 4B, two-dimensional tomographic images along respective scan lines can be obtained.
Further, there is another method called a radial scan as shown in FIG. 5A. In the radial scan, a one-dimensional scan along a scan line extending radially (B-scan) is performed repeatedly while moving in a circumferential direction to other scan lines (C-scan). Due to this, as shown in FIG. 5B, two-dimensional tomographic images along respective scan lines can be obtained.
In the conventional anterior eye three-dimensional image processing apparatus, an examiner inputted, point by point, a position of a scleral spur (SS position) in each of two-dimensional tomographic images of respective sliced surfaces obtained as mentioned above, as a result of which an angle portion (contact portion of a rear surface of a cornea and a front surface of an iris) which is closed beyond the SS position could be displayed as an iridotrabecular contact (ITC) in a chart form.
A configuration of the conventional anterior eye three-dimensional image processing apparatus required the examiner to input, point by point, the SS position in each two-dimensional tomographic image. Therefore, there was a problem that even if the anterior eye OCT could obtain more than a hundred two-dimensional tomographic images, a large amount of time was taken until a start of creating the chart showing the ITC such that it was difficult to use the apparatus in clinical practice.
In order to address such problem, the present applicant proposed an improved anterior eye three-dimensional image processing apparatus in Japanese Patent Application Publication No. 2015-066084. The anterior eye three-dimensional image processing apparatus disclosed therein is configured to identify SS positions by using at least two representative images among a plurality of two-dimensional tomographic images constituting a three-dimensional image, calculate a reference perfect circle passing through at least three SS positions among the identified SS positions, and then based on the calculated reference perfect circle of the representative images, identify SS positions in non-representative images other than the at least two representative images among the plurality of two-dimensional tomographic images.
In the anterior eye three-dimensional image processing apparatus disclosed in Japanese Patent Application Publication No. 2015-066084 filed earlier by the present applicant, by simply inputting, point by point, the at least three SS positions in the two two-dimensional tomographic images, SS positions in all of the other two-dimensional tomographic images constituting the anterior three-dimensional image can be automatically identified. Due to this, the examiner came to be able to omit the point-by-point input of SS positions, and thus for example, the time taken until the start of creating the chart showing the ITC could be drastically reduced.
Afterwards, as a result of further study and experiments which had been done by the inventors of the present disclosure, an anterior eye three-dimensional image processing apparatus capable of automatically identifying an SS position more accurately than the anterior eye three-dimensional image processing apparatus disclosed in Japanese Patent Application Publication No. 2015-066084 was invented.